Method of rendering paper sheets locally transparent



March 13, 1928.

' O. POEPPEL METHOD OF RENDERING PAIfER SHEETS LOCALLY TRANSPARENT Filed April 19. 192a S Q E Q (Q A|\|| w. & M Q N Patented Mar. 13, 1928.

UNITED STATES.

PATENT OFFICE.

nn'rnon or RENDERING PAPER snnn'rs LOCALLY TRANSPARENT.

Application filed April 19, 1926, Serial No. 103,141, and in Germany May 20, 1925.

This invention relates to a method of rendering paper sheets locally transparent, for example sheets to be formed into window envelopes.

Heretofore there have been practised two methods of rendering, paper sheets locally transparent.

According to one method the sheet is coated at the required locality with a suitable medium, such for example as lacquer,

resin or oil which is allowed to act at normal temperature on the paper and then allowed to dry. It is an objection to this method that it involves much labour and the occupation of much space and time, in that for the drying alone as much as 36 hours may be required. It is only when the peration is about completed that its success can be determined.

According to the second method the sheet is coated in a lacquering machine at the desired locality and over a selected area with a medium adapted to render the paper transparent, whereupon a gripping member deposits thecoated sheet on a conveyor band which conveys it to an artificially heated chamber, for example a drying oven. This mechanical method can be performed in much less time than that first described, but is open to the objection that the artificial heat affects deleteriously those parts of the paper which are not coated with the medium,

modifying the color or shade of the paper if colored, or turning white paper yellow.

The method forming the subject of the present invention avoids the objections aforesaid, in that, as contrasted with the first method, it represents a saving of labour, space and time, and, as contrasted'with the second method, it does not involve subjection of the uncoated paper to the influence of artificial heat with consequent risk of discoloration.

Accordin to the invention paper sheets,

which have een coated locally with medium paper cross section diagrammatically illustrating an apparatus by which the invention may be carried into effect.

After the paper sheets a have been coated at the desired locality over a predetermined area with medium adapted to render the paper transparent, for example ina rotary printing and lacquering machine, they are transferred successively from the coating or lacquering machine to a conveyor band 12 into which are built heating elements 6, which may, for example, be electrically heated, and which correspond in form and dimcnsions to the windows to be formed. The conveyor is operatively connected with the lacqucring machine so that it brings a heating element a into position beneath a sheet ever time a. sheet a is deposited on the band, the heating elements being positioned to register with the localities coated with medium, The heating elements are smaller in size than the sheets a, or the parts of such sheets which are to be coated, so that the entire sheets are not heated; but only the desired window parts thereof. The sheets a are held against the band b'by any suitable means, as by the conventionally represented grippers g. The surface of each heating element e is located at a desired distance d beneath-the upper surface of the band, so that the paper does not come directl in contact with the hot surface. The paper sheets travel with the band (to the right) until they are tilted, at a point over the right hand roller r, into a receiver la in which they are piled. The time taken from the application of the coating to each sheet until its transference to the receiver.

can be so regulated that the coating medium is perfectly dried before being discharged into the receiver of receptacle k. The time involved may be a fraction of a minute.

The endless conveyor band, with the builtin' heating-elements, is looped over two rollers 1", 1' connected by a chain f, the rollers 1- being driven from the coating or lacquering machineh. The weight of the band and of the heating elements between the rollers is supported by rails or bands 8 which may also serve as conductors for transferring current to the elements a through, the medium of conductors z.

The distance d may be adjusted accord ing to the nature of the coating medium, the thickness of the paper and the tempera.-

ture of the heating elements.

It is to be understood that the invention heating elements each of the form and di- 1 is not limited to the use of apparatus such mensions corresponding to those of the as described and shown. windows to be formed, and maintaining I claim: the sheets subject to such influence until the In the treatment of paper sheets to render paper is transparent and the coating the same locally transparent, transferring medium completely dried. 15 the sheets, precoated at the desired locality In testimony whereof I have signed my with medium to render the paper transparname to this specification. ent, to the field of influence of travelling OTTO POEPPEL. 

